[DOCS] Quick Start Guide PT2E Example does not work as is. Undefined objects

PT2E example in quick start guide does not work as is. Many undefined objects. No import for `convert_pt2e` and `example_inputs` is not defined for example. Also some indentation issues.

See:
https://docs.pytorch.org/ao/0.13/quick_start.html#pytorch-2-export-quantization